1. Field of the Invention
The present invention relates to a profile clamp and a method for manufacturing the profile clamp. More specifically, the present invention relates to a profile clamp, having conical side walls that are bent radially inwardly, for connecting components that have flanges at their respective ends.
2. Discussion of the Related Art
Profile clamps, per sxc3xa9, are known, for example, from German Reference DE 30 38 491 C2, U.S. Pat. Nos. 3,498,649, 3,964,773, French Reference No. 1,016,629 and from the brochures xe2x80x9cNORMA Conical Flange Jointsxe2x80x9d, (copyright) 1979 and 1988, xe2x80x9cNORMA Profile Clamp with Conical Flangexe2x80x9d,(copyright) November 1996. These known profile clamps are made of ferritic or pure austenitic steel. They are manufactured by pure cold forming, with subsequent welding. These steel profile clamps are not stable at relatively high temperatures. Alternatively, they have too high of a coefficient of thermal expansion [18xc3x9710xe2x88x926 to 22xc3x9710xe2x88x926 m/mxc2x0 C. (for austenitic, creep-resistant steels)], which causes loss of elasticity at high temperatures and, thus, leakages in the joint.
The housings of turbochargers for large diesel engines or gas turbines are currently made of ferritic casting materials which, in the range of 20xc2x0 C. to 600xc2x0 C., have a coefficient of thermal expansion that ranges from 10xc3x9710xe2x88x926 to 14xc3x9710xe2x88x926 m/mxc2x0 C. as the temperature changes. Thus, the known profile clamps, which are made of ferritic or pure austenitic steel, are not suited to join the housing or other components of turbo chargers because the joint would leak at temperatures up to 750xc2x0 due to the excessively high coefficients of thermal expansion of the conventional clamp material. Leaking joints will, among other things, lead to a substantial loss of output from the turbochargers.
In addition, a leaking or loosening connection constitutes a security risk, because turbochargers that have been assembled with these clamps could burst as a result of the loose connection, thereby increasing the risk of injury.
It is an object of the present invention to provide a profile clamp and a method for manufacturing the profile clamp that may be used to reliably secure ferritic, pearlitic casting materials of components through which hot gas flows while meeting the desired requirements of tightness and stability in a temperature range up to 750xc2x0 C.
These and other objects are achieved with a profile clamp made of a martensitic steel, which, at an ambient temperature of 20xc2x0 C. to 750xc2x0 C., has a coefficient of thermal expansion that is at least 0.3xc3x9710xe2x88x926 m/mxc2x0 C. lower than that of a ferritic casting material.
Martensitic steel has a high degree of hardness at very high temperatures and, therefore, withstands high forces that are exerted on the point of junction without being deformed. Furthermore, as a result of the selection of the coefficient of thermal expansion, the profile clamp expands slightly less than the components that are being joined, which are made of a ferritic casting material. The clamping force exerted by the profile clamp on the flanges of the components to be joined increases as the temperature of the joint rises, thereby ensuring that the components will be held together not only due to the lower deformability of the profile clamp, but also because the clamping force increases with rising temperature. Thus, in use, the profile clamp according to the present invention not only avoids the dangers described above, but also avoids the costly manner that is currently used to bolt known profile clamps, which may include the use of additional clamping rings that are fitted with holes for the insertion of screws to further secure the joint.
The profile clamp is made of a steel that is comprised of iron as its main constituent. The remaining constituents, in percentage by weight, are as follows: up to 0.45% C, up to 2.0% Si, up to 2.0% Mn, up to 0.04% P, up to 0.04% S, 15 to 20% Cr, from 1 to 8% Ni, up to 2.5% Mo, up to 0.5% V, up to 0.1% Al, up to 0.1% Co, up to 0.4% Cu, up to 0.4% Pb, up to 0.1% Se,up to 0.1% Te, up to 0.5% Ti, up to 0.1% W, up to 0.05% Zr, up to 0.01% O, up to 0.01% N, up to 0.1% Bi, up to 0.001% B, up to 0.05% Nb.
In a currently preferred exemplary embodiment, the maximum amount of C is 0.4%, of Si is 0.5%, of Mn is 0.8% and of Mo is 2.0%, and the minimum amount of Ni is 1.0%, of Mo is 0.3% and of V is 0.25%.
The profile clamp in one exemplary embodiment of the present invention has at least one clamping band with its end sections being bent radially outwardly and back to form loops. The ends of the end sections are welded to the clamping band. A bolt is disposed in each loop. Each loop has a slit that extends around a major portion of the bolt. The bolts in adjacent loops are connected by a headed clamping bolt. The clamping bolt shaft extends through the slits in the loops. At least one circular ring segment is welded to a radial inner surface of the clamping band. The circular ring segment has conical side walls so that, in axial cross-section, the ring segment is approximately hat-shaped. The conical side walls are fitted with a plurality of reinforcements. One of the bolts disposed within the loops has, in axial cross-section, an approximately tear drop shape with its sides enclosing a right angle. One of the sides of the tear drop shaped bolt extends radially outwardly away from the clamp circumference and the other side extends approximately in the circumferential direction of the clamp. The loop enveloping the tear drop shaped bolt has a matching cross sectional shape. The clamping bolt head is supported on the side of this matching loop that extends radially outwardly and away from the clamp circumference. The profile clamp according to this embodiment withstands, on the basis of its shape alone, very high axial forces, such as may occur in profile clamps with diameters of up to 500 mm and higher. Nevertheless, the clamping band is sufficiently flexible to adapt perfectly to the diameter of the flanges of the components to be joined together because of the separate construction of the semi-circular profiled ring segments and their connection to the clamping band in a circumferential direction. Because the clamping bolt head is supported on the side of the loop, the width of the slit formed in this loop is smaller than in known profile clamps where the clamping bolt head is supported directly on the bolt disposed within the loop. Thus, the clamp according to the present invention has a slit width in the loop that is approximately equal to the diameter of the clamping bolt shaft so that the loop can withstand higher tension forces. Additionally, the clamping bolt head is supported on a large surface on an approximately radially extending side of the loop, without putting stress on the loop with the edge of the clamping bolt head.
In accordance with an alternate exemplary embodiment of the profile clamp according to the present invention, the clamp has at least one circular ring segment having end sections that are bent radially outwardly and back to form loops at each end section. The end sections are welded to the circular ring segment. A bolt is disposed within each of the loops. Each loop has a slit extending around a major portion of the bolt. The bolts in adjacent loops are connected by a headed clamping bolt. The clamping bolt shaft extends through the slits in the loops. The circular ring segment includes conical side walls so that, in axial cross-section, the ring segment is approximately hat-shaped. The conical side walls have a plurality of reinforcements. One of the bolts in the adjacent loops has, in axial cross-section, an approximately tear drop shape with its sides enclosing a right angle. One of the sides of the bolt extends approximately radially outwardly away from the clamp circumference and the other side extends in the circumferential direction of the clamp. The loop surrounding the tear drop shaped bolt has a matching cross-sectional shape. The clamping bolt head is supported on a side of the matching shape loop that extends radially outwardly away from the clamp circumference. In this embodiment, one circular ring segment may be used, as opposed to two, if slightly lower joining forces can be applied by the profile clamp on the components to be joined.
The reinforcements are preferably made of sheet metal and are welded to the conical side walls. These sheet metal reinforcements ensure that the side walls have a very high flexural strength.
A plain washer, having a diameter larger than that of the head of the headed clamping bolt, is disposed between the head of the headed clamping bolt and the loop. Such a plain washer facilitates not only the tightening of the clamp bolt, but also reduces the surface pressure between the clamping bolt head and the side of the loop.
The method for manufacturing the profile clamp according to the present invention includes the material being prequenched and tempered while in the form of a strip. Thereafter, the clamping band is shaped and welded. The welds are subject to an induction tempering treatment for structural homogenization of the profile clamp. By prequenching and tempering, optimal technological properties are obtained in the steel. The induction tempering, which preferably occurs after controlled cooling of the welds, avoids or at least reduces the risk of crack formation in the area of the welds.
The induction tempering treatment is preferably a short-term spheroidization that takes place for less than 5 minutes. The spheroidization preferably occurs in the range of the Ac1 temperature, which results in optimal structural formation in the welding zones.